/*
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* Copyright (C) 2011 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef ART_COMPILER_UTILS_ASSEMBLER_H_
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#define ART_COMPILER_UTILS_ASSEMBLER_H_
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#include <vector>
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#include <android-base/logging.h>
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#include "arch/instruction_set.h"
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#include "arch/instruction_set_features.h"
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#include "arm/constants_arm.h"
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#include "base/arena_allocator.h"
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#include "base/arena_object.h"
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#include "base/array_ref.h"
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#include "base/enums.h"
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#include "base/macros.h"
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#include "base/memory_region.h"
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#include "dwarf/debug_frame_opcode_writer.h"
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#include "label.h"
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#include "managed_register.h"
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#include "mips/constants_mips.h"
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#include "offsets.h"
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#include "x86/constants_x86.h"
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#include "x86_64/constants_x86_64.h"
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namespace art {
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class Assembler;
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class AssemblerBuffer;
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// Assembler fixups are positions in generated code that require processing
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// after the code has been copied to executable memory. This includes building
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// relocation information.
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class AssemblerFixup {
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public:
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virtual void Process(const MemoryRegion& region, int position) = 0;
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virtual ~AssemblerFixup() {}
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private:
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AssemblerFixup* previous_;
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int position_;
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AssemblerFixup* previous() const { return previous_; }
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void set_previous(AssemblerFixup* previous_in) { previous_ = previous_in; }
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int position() const { return position_; }
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void set_position(int position_in) { position_ = position_in; }
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friend class AssemblerBuffer;
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};
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// Parent of all queued slow paths, emitted during finalization
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class SlowPath : public DeletableArenaObject<kArenaAllocAssembler> {
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public:
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SlowPath() : next_(nullptr) {}
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virtual ~SlowPath() {}
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Label* Continuation() { return &continuation_; }
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Label* Entry() { return &entry_; }
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// Generate code for slow path
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virtual void Emit(Assembler *sp_asm) = 0;
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protected:
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// Entry branched to by fast path
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Label entry_;
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// Optional continuation that is branched to at the end of the slow path
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Label continuation_;
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// Next in linked list of slow paths
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SlowPath *next_;
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private:
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friend class AssemblerBuffer;
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DISALLOW_COPY_AND_ASSIGN(SlowPath);
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};
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class AssemblerBuffer {
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public:
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explicit AssemblerBuffer(ArenaAllocator* allocator);
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~AssemblerBuffer();
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ArenaAllocator* GetAllocator() {
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return allocator_;
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}
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// Basic support for emitting, loading, and storing.
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template<typename T> void Emit(T value) {
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CHECK(HasEnsuredCapacity());
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*reinterpret_cast<T*>(cursor_) = value;
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cursor_ += sizeof(T);
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}
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template<typename T> T Load(size_t position) {
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CHECK_LE(position, Size() - static_cast<int>(sizeof(T)));
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return *reinterpret_cast<T*>(contents_ + position);
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}
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template<typename T> void Store(size_t position, T value) {
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CHECK_LE(position, Size() - static_cast<int>(sizeof(T)));
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*reinterpret_cast<T*>(contents_ + position) = value;
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}
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void Resize(size_t new_size) {
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if (new_size > Capacity()) {
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ExtendCapacity(new_size);
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}
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cursor_ = contents_ + new_size;
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}
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void Move(size_t newposition, size_t oldposition, size_t size) {
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// Move a chunk of the buffer from oldposition to newposition.
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DCHECK_LE(oldposition + size, Size());
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DCHECK_LE(newposition + size, Size());
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memmove(contents_ + newposition, contents_ + oldposition, size);
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}
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// Emit a fixup at the current location.
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void EmitFixup(AssemblerFixup* fixup) {
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fixup->set_previous(fixup_);
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fixup->set_position(Size());
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fixup_ = fixup;
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}
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void EnqueueSlowPath(SlowPath* slowpath) {
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if (slow_path_ == nullptr) {
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slow_path_ = slowpath;
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} else {
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SlowPath* cur = slow_path_;
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for ( ; cur->next_ != nullptr ; cur = cur->next_) {}
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cur->next_ = slowpath;
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}
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}
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void EmitSlowPaths(Assembler* sp_asm) {
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SlowPath* cur = slow_path_;
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SlowPath* next = nullptr;
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slow_path_ = nullptr;
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for ( ; cur != nullptr ; cur = next) {
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cur->Emit(sp_asm);
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next = cur->next_;
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delete cur;
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}
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}
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// Get the size of the emitted code.
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size_t Size() const {
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CHECK_GE(cursor_, contents_);
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return cursor_ - contents_;
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}
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uint8_t* contents() const { return contents_; }
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// Copy the assembled instructions into the specified memory block
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// and apply all fixups.
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void FinalizeInstructions(const MemoryRegion& region);
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// To emit an instruction to the assembler buffer, the EnsureCapacity helper
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// must be used to guarantee that the underlying data area is big enough to
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// hold the emitted instruction. Usage:
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//
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// AssemblerBuffer buffer;
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// AssemblerBuffer::EnsureCapacity ensured(&buffer);
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// ... emit bytes for single instruction ...
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#ifndef NDEBUG
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class EnsureCapacity {
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public:
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explicit EnsureCapacity(AssemblerBuffer* buffer) {
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if (buffer->cursor() > buffer->limit()) {
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buffer->ExtendCapacity(buffer->Size() + kMinimumGap);
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}
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// In debug mode, we save the assembler buffer along with the gap
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// size before we start emitting to the buffer. This allows us to
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// check that any single generated instruction doesn't overflow the
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// limit implied by the minimum gap size.
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buffer_ = buffer;
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gap_ = ComputeGap();
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// Make sure that extending the capacity leaves a big enough gap
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// for any kind of instruction.
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CHECK_GE(gap_, kMinimumGap);
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// Mark the buffer as having ensured the capacity.
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CHECK(!buffer->HasEnsuredCapacity()); // Cannot nest.
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buffer->has_ensured_capacity_ = true;
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}
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~EnsureCapacity() {
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// Unmark the buffer, so we cannot emit after this.
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buffer_->has_ensured_capacity_ = false;
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// Make sure the generated instruction doesn't take up more
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// space than the minimum gap.
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int delta = gap_ - ComputeGap();
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CHECK_LE(delta, kMinimumGap);
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}
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private:
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AssemblerBuffer* buffer_;
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int gap_;
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int ComputeGap() { return buffer_->Capacity() - buffer_->Size(); }
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};
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bool has_ensured_capacity_;
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bool HasEnsuredCapacity() const { return has_ensured_capacity_; }
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#else
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class EnsureCapacity {
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public:
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explicit EnsureCapacity(AssemblerBuffer* buffer) {
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if (buffer->cursor() > buffer->limit()) {
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buffer->ExtendCapacity(buffer->Size() + kMinimumGap);
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}
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}
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};
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// When building the C++ tests, assertion code is enabled. To allow
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// asserting that the user of the assembler buffer has ensured the
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// capacity needed for emitting, we add a dummy method in non-debug mode.
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bool HasEnsuredCapacity() const { return true; }
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#endif
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// Returns the position in the instruction stream.
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int GetPosition() { return cursor_ - contents_; }
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size_t Capacity() const {
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CHECK_GE(limit_, contents_);
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return (limit_ - contents_) + kMinimumGap;
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}
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// Unconditionally increase the capacity.
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// The provided `min_capacity` must be higher than current `Capacity()`.
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void ExtendCapacity(size_t min_capacity);
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private:
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// The limit is set to kMinimumGap bytes before the end of the data area.
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// This leaves enough space for the longest possible instruction and allows
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// for a single, fast space check per instruction.
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static const int kMinimumGap = 32;
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ArenaAllocator* const allocator_;
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uint8_t* contents_;
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uint8_t* cursor_;
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uint8_t* limit_;
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AssemblerFixup* fixup_;
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#ifndef NDEBUG
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bool fixups_processed_;
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#endif
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// Head of linked list of slow paths
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SlowPath* slow_path_;
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uint8_t* cursor() const { return cursor_; }
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uint8_t* limit() const { return limit_; }
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// Process the fixup chain starting at the given fixup. The offset is
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// non-zero for fixups in the body if the preamble is non-empty.
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void ProcessFixups(const MemoryRegion& region);
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// Compute the limit based on the data area and the capacity. See
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// description of kMinimumGap for the reasoning behind the value.
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static uint8_t* ComputeLimit(uint8_t* data, size_t capacity) {
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return data + capacity - kMinimumGap;
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}
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friend class AssemblerFixup;
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};
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// The purpose of this class is to ensure that we do not have to explicitly
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// call the AdvancePC method (which is good for convenience and correctness).
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class DebugFrameOpCodeWriterForAssembler final
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: public dwarf::DebugFrameOpCodeWriter<> {
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public:
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struct DelayedAdvancePC {
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uint32_t stream_pos;
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uint32_t pc;
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};
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// This method is called the by the opcode writers.
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void ImplicitlyAdvancePC() final;
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explicit DebugFrameOpCodeWriterForAssembler(Assembler* buffer)
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: dwarf::DebugFrameOpCodeWriter<>(/* enabled= */ false),
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assembler_(buffer),
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delay_emitting_advance_pc_(false),
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delayed_advance_pcs_() {
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}
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~DebugFrameOpCodeWriterForAssembler() {
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DCHECK(delayed_advance_pcs_.empty());
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}
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// Tell the writer to delay emitting advance PC info.
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// The assembler must explicitly process all the delayed advances.
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void DelayEmittingAdvancePCs() {
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delay_emitting_advance_pc_ = true;
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}
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// Override the last delayed PC. The new PC can be out of order.
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void OverrideDelayedPC(size_t pc) {
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DCHECK(delay_emitting_advance_pc_);
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if (enabled_) {
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DCHECK(!delayed_advance_pcs_.empty());
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delayed_advance_pcs_.back().pc = pc;
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}
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}
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// Return the number of delayed advance PC entries.
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size_t NumberOfDelayedAdvancePCs() const {
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return delayed_advance_pcs_.size();
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}
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// Release the CFI stream and advance PC infos so that the assembler can patch it.
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std::pair<std::vector<uint8_t>, std::vector<DelayedAdvancePC>>
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ReleaseStreamAndPrepareForDelayedAdvancePC() {
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DCHECK(delay_emitting_advance_pc_);
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delay_emitting_advance_pc_ = false;
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std::pair<std::vector<uint8_t>, std::vector<DelayedAdvancePC>> result;
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result.first.swap(opcodes_);
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result.second.swap(delayed_advance_pcs_);
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return result;
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}
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// Reserve space for the CFI stream.
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void ReserveCFIStream(size_t capacity) {
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opcodes_.reserve(capacity);
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}
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// Append raw data to the CFI stream.
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void AppendRawData(const std::vector<uint8_t>& raw_data, size_t first, size_t last) {
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DCHECK_LE(0u, first);
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DCHECK_LE(first, last);
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DCHECK_LE(last, raw_data.size());
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opcodes_.insert(opcodes_.end(), raw_data.begin() + first, raw_data.begin() + last);
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}
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private:
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Assembler* assembler_;
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bool delay_emitting_advance_pc_;
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std::vector<DelayedAdvancePC> delayed_advance_pcs_;
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};
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class Assembler : public DeletableArenaObject<kArenaAllocAssembler> {
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public:
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// Finalize the code; emit slow paths, fixup branches, add literal pool, etc.
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virtual void FinalizeCode() { buffer_.EmitSlowPaths(this); }
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// Size of generated code
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virtual size_t CodeSize() const { return buffer_.Size(); }
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virtual const uint8_t* CodeBufferBaseAddress() const { return buffer_.contents(); }
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// CodePosition() is a non-const method similar to CodeSize(), which is used to
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// record positions within the code buffer for the purpose of signal handling
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// (stack overflow checks and implicit null checks may trigger signals and the
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// signal handlers expect them right before the recorded positions).
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// On most architectures CodePosition() should be equivalent to CodeSize(), but
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// the MIPS assembler needs to be aware of this recording, so it doesn't put
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// the instructions that can trigger signals into branch delay slots. Handling
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// signals from instructions in delay slots is a bit problematic and should be
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// avoided.
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virtual size_t CodePosition() { return CodeSize(); }
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// Copy instructions out of assembly buffer into the given region of memory
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virtual void FinalizeInstructions(const MemoryRegion& region) {
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buffer_.FinalizeInstructions(region);
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}
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// TODO: Implement with disassembler.
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virtual void Comment(const char* format ATTRIBUTE_UNUSED, ...) {}
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virtual void Bind(Label* label) = 0;
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virtual void Jump(Label* label) = 0;
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virtual ~Assembler() {}
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/**
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* @brief Buffer of DWARF's Call Frame Information opcodes.
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* @details It is used by debuggers and other tools to unwind the call stack.
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*/
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DebugFrameOpCodeWriterForAssembler& cfi() { return cfi_; }
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ArenaAllocator* GetAllocator() {
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return buffer_.GetAllocator();
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}
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AssemblerBuffer* GetBuffer() {
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return &buffer_;
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}
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protected:
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explicit Assembler(ArenaAllocator* allocator) : buffer_(allocator), cfi_(this) {}
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AssemblerBuffer buffer_;
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DebugFrameOpCodeWriterForAssembler cfi_;
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};
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} // namespace art
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#endif // ART_COMPILER_UTILS_ASSEMBLER_H_
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